1. Field of the Invention
The present invention relates to a thin-film magnetic head to be mounted in a magnetic recording and reproducing apparatus and the like, and more particularly, to a thin-film magnetic head having a magnetoresistive device composed of a laminate of a magnetic layer, a non-magnetic conductive layer and a magnetic layer to detect changes in a leakage magnetic field from a recording medium in what is called the spin valve method.
2. Description of the Related Art
Thin-film magnetic heads of what is called the spin valve type have been provided to magnetically reproduce signals recorded on a recording medium at high density, and one example of such magnetic heads is disclosed in, for example, U.S. Pat. No. 5,159,513.
The spin valve thin-film magnetic head comprises a magnetoresistive device 4 having a sandwich structure composed of a first magnetic layer 1, a non-magnetic conductive layer 2 and a second magnetic layer 3 as shown in FIG. 2. An antiferromagnetic layer 5 is further provided on the first magnetic layer 1, and exchange anisotropic coupling between the first magnetic layer 1 and the antiferromagnetic layer 5 fixes the magnetization direction of the magnetic layer 1 in one direction. When a leakage magnetic field is applied from a recording medium on which magnetic signals are recorded, the magnetization direction is changed in the second magnetic layer 3, and the electric resistance varies according to the angle formed between the magnetization directions of the first magnetic layer 1 and the second magnetic layer 3. The electric resistance is lowest when the magnetization directions of the magnetic layers 1 and 3 are parallel, and is highest when the magnetization directions are antiparallel.
FIG. 3 shows the relationship between the leakage magnetic field M applied to the magnetoresistive device 4 and the electric resistance R. When a stationary current is applied to the magnetoresistive device 4, detection voltage changes in response to changes .delta. in the electric resistance. The change in the leakage magnetic field from the recording medium is detected based on the detection voltage, and the magnetic signals are reproduced as electric signals.
In order to obtain a reproduction output voltage changing smoothly in response to the change in the leakage magnetic field from the recording medium in the aforesaid thin-film magnetic head, the angle between the magnetization directions of the first and second magnetic layers 1 and 3 is required to change smoothly in response to the change in the leakage magnetic field from the recording medium.
However, if the second magnetic layer 3 has a multi-domain structure, the domain structure is changed owing to the change in the leakage magnetic field from the recording medium. Rapid movement of domain walls when the domain structure changes makes the magnetization angle, which changes in response to the changes in the leakage magnetic field, discontinuously jump. Therefore, the angle between the magnetization directions of the first and second magnetic layers 1 and 3 does not change continuously in response to the change in the leakage magnetic field from the recording medium, and discontinuous or irregular jumps of the magnetization rotation angle occur. This causes discontinuous or irregular jumps in the voltage of the stationary current, that is, the reproduction voltage, which result in Barkhausen noises n shown in FIG. 3.